Internal erosion induces alterations in the initial microstructure of soils, simultaneously affecting physical, hydraulic, and mechanical properties. The initial soil composition plays a crucial role in governing the initiation and progression of seepage-induced suffusion. This study employs the controlled variable method to develop granular soil models with varying particle size ratios, initial fine particle contents, and coarse particle shapes. Seepage suffusion simulations coupled with microstructural analyses are conducted using the CFD-DEM approach. Results demonstrate that particle size ratio, fine particle content, and coarse particle shape exert distinct influences on cumulative erosion mass, fine particle distribution, contact fabric, and mechanical redundancy at both macroscopic and microscopic scales. This numerical investigation advances the fundamental understanding of internal erosion mechanisms and informs the development of micro-mechanical constitutive models. Furthermore, for binary granular media composed of coarse and fine particles, careful control of the particle size ratio and fine content is recommended when utilizing gap-graded soils in embankment and dam construction to improve structural resilience and resistance to internal erosion.

This study proposed a novel hybrid resolved framework coupling computational fluid dynamics (CFD) with discrete element method (DEM) to investigate internal erosion in gap-graded soils. In this framework, a fictitious domain (FD) method for clump was developed to solve the fluid flow around realistic-shaped coarse particles, while a semi-resolved method based on a Gaussian-weighted function was adopted to describe the interactions between fine particles and fluid. Firstly, the accuracy of the proposed CFD-DEM was rigorously validated through simulations of flow past a fixed sphere and single ellipsoid particle settling, compared with experimental results. Subsequently, the samples of gap-graded soil considering realistic shape of coarse particles were established, using spherical harmonic (SH) analysis and clump method. Finally, the hybrid resolved CFD-DEM model was applied to simulate internal erosion in gap-graded soils. Detailed numerical analyses concentrated on macro- -micro mechanics during internal erosion, including the critical hydraulic gradient, structure deformation, as well as particle migration, pore flow, and fabric evolution. The findings from this study provide novel insights into the multi-scale mechanisms underlying the internal erosion in gap-graded soils.

This study investigates the simultaneous influence of particle shape and initial suction on the hydromechanical behavior of unsaturated sandy soils. Anisotropic loading-unloading tests at constant water content conditions were conducted on three sands with distinct shapes (Firoozkooh-most angular, Babolsar-Subangular, and Mesr-roundest) using a direct shear apparatus. Particle shapes were quantified in terms of sphericity, roundness, and regularity using the results of scanning electron microscopy (SEM) tests. In addition, a coupled hydromechanical model based on elasto-viscoplasticity was developed and validated against the experimental results first. The model was then employed to conduct a parametric study (compressibility, pore water pressure, and permeability) with an emphasis on the role of particle morphology and shape. The findings revealed rounder particles (higher regularity) experienced higher volumetric strain (epsilon v) under lower suction but less epsilon vwith increasing suction compared to angular sands. Moreover, the rate of permeability reduction during loading in Mesr sand was 1.5 times and 2.4 times higher than that of Babolsar and Firoozkooh sands at near-saturation condition. However, this amount decreased with increasing suction. Pore water pressure (PWP) generation was highest in the most angular sand due to its retention characteristics. The relationship between void ratio and PWP was independent of loading cycles and exhibited a linear dependence. Particle shape significantly impacted this relationship, with rounder sands showing a higher rate of void ratio change per unit change in PWP.

The shape of particles significantly influences their mechanical properties, making accurate shape modeling crucial in numerical simulations. This paper proposes a framework for generating particles by applying improved spherical harmonic reconstructions to convex hull surfaces. The framework integrates mesh refinement tech- niques to enhance mesh resolution, enabling the generation of finer surface details than 3D laser scanning. Three parameters are introduced: Delta K1, which controls roundness; Delta K2, which governs roughness; and Rd, which represents the boundary between roundness and roughness in spherical harmonic reconstructions. Introducing these parameters not only allows independent control over the three levels of shape (form, roundness, and roughness) but also enhances the flexibility of the method, enabling the generation of various particle shapes. Granular assemblies with varying roundness and roughness distributions are generated and applied in discrete element method (DEM) simulations of triaxial shear. The results show that roundness is negatively correlated with the peak friction angle, while roughness is positively correlated. The proposed method enhances the ability to generate complex particle shapes, offering a practical tool for modeling and simulating granular materials.

Particle shape and local breakage significantly affect the deformation characteristics of crushable granular materials. However, in the existing constitutive model research, there is less introduction of particle shape on particle breakage. A quantitative parameter for the three-dimensional particle shape (Average spherical modulus GM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{G_{M}}$$\end{document}) is proposed in this study. Combined with GM\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\overline{G_{M}}$$\end{document}, the triaxial compression test of granular materials with different particle shapes was carried out, and the particle size distribution before and after the test was determined. The results indicate that the local damage mechanism governs the macroscopic deformation behavior of granular materials, as influenced by the particle gradation of the samples before and after the triaxial compression test. Based on these findings, a binary medium model with a friction element weakening factor is proposed. This model incorporates the effects of particle shape and breakage behavior, significantly enhancing its calculation accuracy. Experimental results demonstrate that the model effectively predicts the deformation of crushable granular materials, accounting for particle shape.

This study investigates the impact of fabric anisotropy on the directional filtration mechanisms in granular filters, which arise from inherent particle shape variations and different preparation methods. Using the discrete element method, diverse filter samples underwent extensive numerical filtration tests in different directions. Subsequently, the pore space of these samples was analysed using an extraction algorithm. The results highlight the significant influence of particle shapes and preparation methods on intensifying anisotropy, which in turn remarkably affects directional filtration properties. Analysis of the pore space reveals variations in pore connectivity across different directions, explaining the observed differences in retention coefficients. This study emphasises the need for a comprehensive approach that accounts for constriction size, number, and connectivity to yield precise results. It contributes valuable insights into the role of anisotropy in granular materials, sheds light on complex directional filtration mechanisms, and advances related applications.

The discrete element method (DEM) is adopted to investigate the influence of the particle shape on the smallstrain stiffness and stiffness degradation of granular materials during triaxial compression tests. Clumped particles are used to simulate irregular granular particles. The simulation results show that a more irregular particle shape causes an increase in the initial stiffness at very small strains and more delayed stiffness degradation. The micromechanism is explored on the basis of the analytical stress-force-fabric relationship, which reveals that increased particle irregularity leads to higher relative contribution of the tangential force anisotropy to the deviatoric stress. The achievable slip ratio and the mechanical coordination number also increase with increasing particle irregularity, resulting in larger resistance to deformation. An equivalent spherical particle analysis method is proposed, which reveals that the irregularity of particle shapes significantly increases both the sliding resistance and the rotational resistance between two particles, resulting in greater stability in the contact network and thus contributing to higher macroscopic stiffness and slower stiffness degradation.

The physical and mechanical properties of granular soils are strongly related to the overlying stresses to which they are subjected. In particular, during the engineering construction phase, which involves activities like foundation stacking and building construction, the applied loads on the soil increase continuously over time. Unfortunately, current stress-controlled compression geotechnical tests have not adequately considered this situation. Therefore, this study aims to examine the effects of various factors, including void ratio, confining stress, stress loading rate, and particle shape, on both macroscopic shear properties and microscopic characteristics of granular soils under conditions of increasing axial stress in biaxial compression numerical simulations. The results show that: (1) In stress-controlled tests on granular soils, samples exhibit three different shear behaviors as the void ratio varies; (2) the confining stress and particle shape will change the magnitude of the deviatoric stresses and axial strains in the peak state of the sample, but not their trends; (3) the stress loading rate does not affect the strength of the samples. Therefore, the loading rate can be increased appropriately to improve the computational efficiency of the numerical model. These findings will enhance understanding of the time-dependent behavior of granular soils and provide valuable insights for engineering applications, particularly in soil mechanics, foundation treatment, and slope stability.

In this study, a series of undrained multidirectional cyclic simple shear tests were conducted using the discrete element method. Various stress paths, including figure-8, circular, teardrop, and straight-line shapes, were considered. Realistic and irregular particles were generated by integrating the theory of random fields for spherical topology with the Fourier-shape-based method. The influence of particle shape irregularity was assessed using a synthetic parameter derived from four common descriptors: aspect ratio, roundness, convexity, and sphericity. The study revealed that the liquefaction resistance of samples subjected to a constant cyclic shear stress ratio predominantly depended on the stress trajectory and particle shape. Numerical results demonstrated that the sample undergoing the unidirectional simple shear exhibited the highest liquefaction resistance, whereas the figure-8 shape exhibited the lowest. Furthermore, greater irregularity in particle shape corresponded to increased resistance to failure. Additionally, microstructural evolutions of granular samples were quantified throughout the simulation using the contact-normal-based fabric tensor. This allowed for a comprehensive exploration of the interplay between internal structure and external loading, leading to a more comprehensive understanding of the macroscopic observations discussed above.

The contact network of granular materials is often divided into strong and weak subnetworks, which play different roles in micromechanics. Within the strong contact network, there exists the largest connected component, that is, the largest cluster, which may connect system boundaries and could be the most important structure in force transmission of the whole system. This paper concerns the particular features of the largest cluster in the strong contact network of granular materials, by considering the combining effects of loading path and particle shape. A series of true triaxial tests with various intermediate principal stress ratios are conducted for granular assemblies of different shaped particles using the discrete element method (DEM). Both the macroscopic stress-strain responses and the microscopic topological changes of the contact network are investigated. It is found that both particle shape and loading path will influence the shear strength and the topological features of the strong network. The threshold zeta$\zeta $ (the ratio to the average force) is used to distinguish the strong and weak networks, and a critical threshold can be identified by comparing the network-based metrics. The largest cluster within the strong network approaching the critical threshold can span the boundaries in each direction with minimum contacts, which occupies a small portion of particles and contacts but transmits a considerable portion of the applied stress. In addition, the similar contribution weight of the largest cluster to the deviatoric stress is identified for granular materials with different particle shapes.